Method and device for continuously cutting during hot rolling

ABSTRACT

A method and a device for cutting a rolled strip which runs out from a hot-rolling mill train, especially at particularly high speed, is described. The rolled strip is cut by shears arranged downstream of the hot-rolling mill train, a driver having two driver rollers being arranged downstream of the shears, the rolled strip running through between the driver rollers, and the rolls of the driver being driven open subsequent to the cutting.

FIELD OF THE INVENTION

The present invention relates to a method and a device for cutting ametal strip which runs out from a hot-rolling mill train, especially atparticularly high speed. The metal strip is cut by shears arrangeddownstream of the hot-rolling mill train. A driver having two driverrollers is arranged downstream of the shears. The metal strip runsthrough the driver rollers.

BACKGROUND INFORMATION

In hot rolling, special requirements exists with respect to the cuttingof metal strips, since hot rolling takes place at high strip speeds.Consequently, the cutting of a hot-rolled strip must be carried out at ahigh strip speed, as well. Due to the cutting at high speeds, anextremely short time is available for changing over from the conditionsduring the threading out of the front strip to the conditions necessaryfor threading in the rear strip. In particular, the speed of the driverrollers downstream of the shears downstream of the shears must changevery quickly. Therefore, the drivers are required to have extremely lowinertia. However, these requirements can only be met partially so thatnarrow limits are set on the cutting of hot-rolled strips with respectto the strip speed. During the cutting of fast metal strips,particularly when working with strips running out from a roll stand at aspeed above 12 m/sec, a particular problem lies in the repercussions onthe rolling process upstream of the shears.

Japanese Patent JP 8 90058 describes a method for cutting a metal stripin which, subsequent to the cutting, rollers arranged downstream areopened for passing the strip. British Patent No. GB 20 73 080 andJapanese Patent No. 4 171116 describe cutting of rolled strip which runsout from a mill train at high speed.

SUMMARY

An object of the present invention is to provide a method for cuttingfast-running metal strips from a hot strip mill. Repercussions on anupstream mill train by the cutting of the metal strip are prevented orsignificantly reduced.

In the method according to the present invention, driver rollers on bothsides of the shears are utilized. In the sequence of phases according tothe present invention, the driver rollers downstream of the shears canbe opened or closed subsequent to the cutting, the front tension thenbeing guaranteed by the driver rollers upstream of the shears. In thismanner, repercussions on the upstream rolling process due to the cuttingcan be prevented to the greatest possible extent. Thus, qualityimpairments of the rolled metal strip due to the cutting operation canbe reduced. Cutting is now possible at high speeds, as well, withoutrequiring parameters which cannot or only difficulty be achieved from astandpoint of mechanical engineering to be adjusted at the drivers.

In the present invention, the processes are decoupled by reducing thefront tension in the metal strip between the driver rollers and thecoiler prior to opening the driver rollers. In this manner, aparticularly smooth strip run is achieved. Finally, the presentinvention has the advantage that the front tension of the metal stripbetween the driver rollers and driver rollers arranged upstream of theshears is reduced to a necessary minimum tension prior to cutting themetal strip. This further reduces the repercussions of the cutting onthe rolling process, and results in a particularly accurate cut.

In this context, the necessary minimum tension is the tension in themetal strip which is required for the metal strip to be tightened and tobe able to be cut.

In an example embodiment of the present invention, the rear metal stripresulting from the cutting of the metal strip is grasped by the coilersubsequent to opening the driver rollers. After the rear metal strip isgrasped by the coiler, the driver rollers may be closed.

In the example device according to the present invention, driver rollersare provided upstream of and downstream of the shears. In this manner,in connection with the present invention, a particularly good decouplingbetween cutters and rolls is achieved. Advantageously, provision is madefor a computing device which is connected to all system components via adata link.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an exemplary embodiment of a cutting device according tothe present invention.

FIG. 2 shows an exemplary embodiment of a speed controller according tothe present invention.

FIG. 3 shows a torque curve.

FIG. 4 shows a tensile stress curve.

DETAILED DESCRIPTION

In the following description of an exemplary embodiment of the presentinvention, the following abbreviations are used:

DC upcoiler PR1 driver rollers upstream of the shears PR2 driver rollersdownstream of the shears WR working roll b_(strip) strip width F_(i)front tension upstream of system component 1 h_(strip) strip thicknessJ_(i) moment of inertia of the rollers including transmission, motor,etc. L_(i) length between two neighboring system components upstream ofcomponent 1 M_(FF, i) predefined torque M_(i) motor torque M_(N, i)rated torque of motor M_(Rel%, i) relative motor torque in % related tothe rated torque R_(i) roller radius V_(Add, i) additional setpointvalue of the speed or of the roller circumferential speed V_(i) speed orroller circumferential speed V_(i)* setpoint value of speed or rollercircumferential speed V_(strip) normal value of the strip speed σ_(i)specific front tension upstream of system component 1 σM_(FF, i)predefined torque converted into specific front tension σM_(i) motortorque converted into specific front tension σ_(OP, i) specific fronttension in the operating point upstream of system component 1 t time

Index i designates the system components upcoiler (DC), driver rollers(PR1) upstream of the shears, driver rollers (PR2) or working rolls (WR)of the last stand of a mill train upstream of the cut adjustment.

FIG. 1 shows a cutting device having shears 10, a stand with driverrollers PR1 upstream of shears 10, a stand with driver rollers PR2downstream of shears 10, a coiler DC, as well as a computing device 11.Computing device 11 is connected by a data link via a data line 12 tothe drives of driver rollers PR1 and PR2, of coiler DC, and of shears10, the data line being designed in an exemplary embodiment of the bussystem.

In FIG. 1, reference symbol 1 designates a metal strip, and the arrowdesignated by reference symbol 2 refers to the running direction ofmetal strip 1. Seen in the running direction of metal strip 1, a milltrain for rolling metal strip 1 is arranged upstream of the cuttingdevice. In this context, WP designates the working rolls of the laststand of this mill train.

Subsequent to the cutting of metal strip 1 by shears 10, metal strip 1is divided into a front part 13 and a rear part 14. Coiler DC isdesigned in such a manner that it winds front metal strip 13 and rearmetal strip 14 into different coils.

A motor torque M_(i), where i (i=WR, PR1, PR2, DC), is delivered to thedifferent system components, respectively, i.e., to working rolls WR,driver rollers PR1 and PR2, and to coiler DC. The system reacts to thiswith speeds or roller circumferential speeds v_(i), where i (i=WR, PR1,PR2, DC), and front tensions F_(i) or specific front tensions σ_(i),where i (i=WR, PR1, PR2, DC).

In an exemplary embodiment, system components driver rollers PR1, PR2,and coiler DC each are provided with a speed controller according toFIG. 2, which contains a PI controller 3. Applied to the input of thisPI controller 3 are setpoint speed v_(i)* and actual speed v_(i). Actingon the limiting of this PI controller 3 is a predefined torque M_(FF,i).For simulating secondary current controls, a delay element of secondorder is connected in series to and downstream of PI controller 3, motortorque Mi being yielded at the output of the delay element.

The speed controllers can be operated in 2 modes:

Mode 0 (switch 5 toward the left)

When switch 5 is in this position, PI controller 3 operates as a normalspeed controller, keeping the speed at its setpoint value.

Mode 1 (switch 5 toward the right)

An additional setpoint value V_(Add,i) of the speed or of the velocityis added at the input of PI controller 3. The output of PI controller 3is limited by a one-sided limiting 31. In this manner, in the case of apossible tear of metal strip 1, the speed can increase only to theextent until it deviates from the setpoint value by V_(Add,i). In thisoperating mode, predefined torque M_(FF,i) becomes active immediately asmotor torque M_(i). In this manner, a reliable operation is achieved.

The speed controllers are controlled in that the mode and torqueM_(FF,i) to be added are predefined for the speed controllers. Theseinputs are transmitted to the speed controllers via delay times whichsimulate the real transmission delay times.

To be able to better evaluate motor torque M_(i), the relative motortorque in % is calculated using rated motor torque M_(N,i):${M_{{{Rel}\%},i} = {\frac{M_{i}}{M_{N,i}} \cdot 100}},{i = {WR}},{PR1},{PR2},{DC}$

In an exemplary embodiment, the time characteristic of the cutting ofthe metal strip is divided into the following phases:

Phase 1: starting state;

Phase 2: reduce front tension between PR1 and PR2 to a minimum tension;

Phase 3: cut and compensate for the previously existing minimum tension;

Phase 4: reduce front tension between PR2 and DC;

Phase 5: open PR2 and complete winding of front metal strip 14;

Phase 6: coiler grasps the new strip and builds up tension;

Phase 7: close PR2 and continue to build up coiler tension;

Phase 8: final state=starting state with new strip.

FIG. 3 as well as the following table show how the speed controllers arecontrolled during the individual phases:

Mode Predefined torques [N/mm²] PHASE WR PR1 PR2 DC σM_(FF, PR1)σM_(FF, PR2) σM_(FF, DC) 1 0 1 1 1 0   −4.8 12 2 0 1 1 1 0 → 6  −4.8 →−10.8 12 3 0 1 1 0   6 → 7.2 −10.8    12 → 10.8 4 0 1 1 0 7.2 −10.8 →0    10.8 → 0   5 0 1 0 0 7.2 0   0 6 0 1 0 1 7.2 0    0 → 7.2 7 0 1 1 10     0 → −4.8 7.2 → 12  8 0 1 1 1 0   −4.8 12

To allow the effect of the predefined torques M_(FF,i) on specific fronttorques σ_(i) to be read off directly, values σM_(FF,i) are indicated inN/mm², from which the predefined torques are calculated using theequation

M _(FF,i) =σM _(FF,i) ·b _(strip) ·h _(strip) ·R _(i),

i=WR, PR1, PR2, DC

Correspondingly, it applies to the motor torques that

M _(i) =σM _(i) ·b _(strip) ·h _(strip) ·R _(i),

i=WR, PR1, PR2, DC

Phases 3 and 4 follow each other immediately without time interval sothat the coiler tension is reduced from 12 to 0 N/mm² withoutinterruption. In the same way, phases 6 and 7 follow each otherimmediately so that the coiler tension is built up from 0 to 12 N/mm²using a continuous ramp.

FIG. 4 shows the characteristic of front tensions σ_(PR1) and σ_(PR2)between the working rolls and the driver rollers upstream of the shearsor between the shears and the driver rollers downstream of the shearsover time t. In this context, the following numerical values are takenas a basis:

L_(PR1) = 23955 mm L_(PR2) = 2480 mm L_(DC) = 4715 mm (front metal strip14) = 2272 mm (rear metal strip 13) R_(WR) = 290 mm R_(PR1) = 250 mmR_(PR2) = 250 mm R_(DC) = 1000 mm (front metal strip 14) = 375 mm (rearmetal strip 13) J_(WR) = 21380 kgm² J_(PR1) = 234 kgm² J_(PR2) = 234kgm² J_(DC) = 14351 kgm² (front metal strip 14) = 2495 kgm² (rear metalstrip 13) b_(strip) = 1000 mm h_(strip) = 3 mm v_(strip) = 16 m/sσ_(OP, PR1) = 7.2 N/mm² σ_(OP, PR2) = 7.2 N/mm² σ_(OP, DC) = 12 N/mm²M_(N, WR) = 382000 Nm M_(N, PR1) = 20400 Nm M_(N, PR2) = 20400 NmM_(N, DC) = 50000 Nm

The cutting of metal strip 1 starts at approximately 380 m/sec. Thecharacteristic of tensile stress σ_(PR1) min metal strip 1 betweenworking rolls WR and driver rollers PR1 upstream of shears 10 clearlyshows the effect of the example method according to the presentinvention on the tensile stress downstream of working rolls WR. Duringthe cutting operation, the tensile stress remains nearly constantdownstream of working rolls WR as indicated by FIG. 4. Thus, cuttingprocess and rolling are decoupled, i.e., the cutting of the metal stripdoes not influence the rolling of the metal strip.

We claim:
 1. A method for cutting a metal strip which runs out from ahot-rolling mill train at a high speed, shears for cutting the metalstrip are arranged downstream of the hot-rolling mill train, the shearsbeing provided between upstream driver rollers and downstream driverrollers, the metal strip running between the upstream driver rollers andbetween the downstream driver rollers, the upstream driver rollers andthe downstream driver rollers exerting a holding force on the metalstrip, the upstream driver rollers and downstream driver rollers beingcontrolled by drivers, the method comprising: reducing a front tensionin the metal strip between the downstream driver rollers and thedownstream driver rollers to a minimum tension; after reducing the fronttension, cutting the metal strip; during the cutting, compensating forthe minimum tension; after the cutting, reducing the front tension inthe metal strip between the downstream driver rollers and a coiler; andafter reducing the front tension in the metal strip between thedownstream driver rollers and the coiler, opening the downstream driverrollers so that a holding force is substantially zero.
 2. The methodaccording to claim 1, wherein the cutting step includes dividing themetal strip into a rear metal strip and a front metal strip, the methodfurther comprising: grasping the rear Metal strip by the coiler afteropening the downstream driver rollers.
 3. The method according to claim2, further comprising: closing the downstream driver rollers after thegrasping of the rear metal strip by the coiler.
 4. The method accordingto claim 1, wherein the metal strip runs out from the mill train at aspeed of greater than 12 m/s.